1. Field of the Invention
The present invention relates to a method of and an apparatus for blanking elements of a belt for use in a continuously variable transmission.
2. Description of the Prior Art
Generally, each of elements of a belt for use in a continuously variable transmission (CVT) comprises a body having a V-shaped surface for contact with a pulley of the continuously variable transmission and a head joined to an upper edge of the body. The element also has a pair of recesses defined between the body and the head. A plurality of elements are stacked and bundled into an annular form as the belt by endless rings that are mounted respectively in the recesses. When the belt is completed, the bodies with the V-shaped surfaces are positioned radially inside of the annular form and the heads are positioned radially outside of the annular form.
The elements are blanked out of a metal sheet by a die and a punch. A process of blanking an element out of a metal sheet comprises the steps of blanking an element out of the metal sheet while keeping the element joined to the metal sheet by a connector and separating the element from the metal sheet by cutting off the connector. According to the blanking process, the connector is positioned at two locations, i.e., a central region or tip end of the head and a central region or lower edge of the body, which are not required to be highly accurate dimensionally in the shearing process that is performed in the blanking step. In the blanking step, the V-shaped surface that needs to be of the highest dimensional accuracy of the element is reliably sheared to a desired level of dimensional accuracy.
When the connector is cut off in the separating step, however, a so-called shear drop, which is a thin region whose surface is inclined to the blanking direction, is created in the central region of the head and the central region of the body. If such a shear drop is positioned on the tip end of each of the heads that are located radially outside of the annular form of the belt, then the annular stack of the elements tends to bend toward the heads out of the circumferential direction due to the contact between the shear drops, thus adversely affecting the accuracy with which the elements are stacked.
The body of each of the elements has, on one side thereof, a thin portion for smoothly guiding the stacked elements to bend in the circumferential direction. The thin portion has already been prepared by a pair of corners on the opposite edges of the metal sheet, and serves as a blanking position corresponding to a substantially lower half portion of the body. Since such thin portions are positioned on the respective opposite edges of the metal sheet, a pair of symmetrical elements is blanked out of the metal sheet at the respective positions corresponding to the thin portions. Specifically, a pair of punches is used to blank the respective elements out of the metal sheet such that the thin portions are located at respective predetermined positioned on the elements. In order to keep the blanking positions highly accurately in alignment with the respective thin portions of the metal sheet prior to the blanking step, it is necessary to center the metal sheet to align the center between the blanking positions, i.e., between the punches, with the transverse center of the metal sheet.
Heretofore, it has been customary to center the metal sheet with a pair of guide members such as guide plates or abutment pins on both sides of a feed path for delivering the metal sheet for contacting and positionally limiting the opposite edges of the metal sheet. The guide members are spaced from each other by a distance substantially equal to the width of the metal sheet.
However, if the clearance between the guide members and the opposite edges of the metal sheet is reduced to center the metal sheet highly accurately with the guide members, then the metal sheet as it is delivered is subject to increased resistance due to contact between the metal sheet and the guide members, resulting in a failure to deliver the metal sheet at a high speed.
With the metal sheet having the thin portions on the opposite edges thereof, the width of one of the thin portions may possibly be different from the width of the other thin portion. If the widths of the thin portions are different from each other, then even when the transverse center of the metal sheet is aligned with the center between the punches by the guide members, the thin portions are not located in the desired positions on the bodies, and hence the thin portions of the blanked elements may be positioned differently from each other.
It is therefore an object of the present invention to provide a method of and an apparatus for highly accurately blanking elements of a belt for use in a continuously variable transmission.
To achieve the above object, there is provided in accordance with the present invention a method of blanking elements of a belt for use in a continuously variable transmission, each having a body having opposite side edges which jointly provide a V-shaped surface for contact with a pulley of the continuously variable transmission and a head joined to a first edge of the body, symmetrically out of a metal sheet having a pair of thin portions on respective marginal edges thereof which are joined to a remaining portion of the metal sheet via respective corners, the method comprising the steps of centering the metal sheet by positioning a center between the corners as a center of the metal sheet, blanking the elements out of the metal sheet, the elements remaining joined to the metal sheet by respective connectors which are formed in the respective thin portions of the metal sheet, the bodies having respective second edges remote from the first edge and formed in the respective thin portions of the metal sheet, and separating the elements from the metal sheet by cutting off the connectors along the second edges of the bodies.
In the above method, first, the metal sheet is centered. Since the metal sheet is centered by positioning the center between the corners as the center of the metal sheet, the metal sheet can be centered accurately without being affected by the widths of the thin portions, i.e., the distances from the corners to the opposite edges of the metal sheet.
Then, the elements are blanked out of the metal sheet while they remain joined to the metal sheet by the connectors. The connectors are disposed at the second edges, i.e., lower edges, of the bodies. The V-shaped surface provided by the opposite side edges of each of the bodies is thus reliably sheared off with a sufficient level of accuracy.
Thereafter, the elements are separated from the metal sheet by cutting off the connectors. Since the connectors are disposed between the opposite side edges of the bodies which provide the V-shaped surface, only the connectors are required to be severed between the opposite side edges of the bodies. Because the peripheral edges of the elements have already been sheared highly accurately by this time, no shear drop occurs on the heads as the connectors to be sheared off are not joined to the heads, so that the heads are kept flat as desired. When the elements are stacked, the heads are held in reliable contact with each other, and the stack of the elements does not tend to bend toward the heads out of the circumferential direction, thus increasing the accuracy with which the elements are stacked. Even if a shear drop occurs when the connectors joined to the bodies are cut off, since the bodies are positioned radially inside of the annular form when the elements are stacked into the annular form, the shear drop does not adversely affect the accuracy with which the elements are stacked, and hence the elements can be stacked well in the circumferential direction.
The step of blanking the elements comprises the step of blanking the elements out of the metal sheet so as to be displaced in a blanking direction by a distance equal to at least the thickness of the metal sheet between the corners, the connectors being inclined and joined to the blanked elements which lie substantially parallel to the metal sheet.
Inasmuch as the elements are blanked out of the metal sheet so as to be displaced in a blanking direction by a distance equal to at least the thickness of the metal sheet between the corners, the elements are prevented from being fitted again in holes, complementary in shape to the elements, defined in the metal sheet after the elements are blanked.
The step of blanking the elements comprises the step of forming the connectors each having a width which is 1 to 3 times the thickness of the metal sheet between the corners.
The elements blanked out of the metal sheet remain joined to the metal sheet by the connectors formed in the thin portions which are thinner than the metal sheet between the corners. If the width of the connectors were smaller than the thickness of portion of the metal sheet between the corners, then the connectors would be bent or crack due to the weight of the elements, and the elements might possibly come off the metal sheet when the metal sheet is delivered to the separating step. In this case, the elements could not be separated from the metal sheet highly accurately by cutting off the connectors. If the width of the connectors were greater than a width that is 3 times the thickness of portion of the metal sheet between the corners, then the connectors would pose increased resistance to the cutting off of the connectors, preventing the elements from being smoothly separated from the metal sheet or possibly deforming the elements due to forces applied when severing the connectors.
According to the present invention, as described above, the width of the connectors is 1 to 3 times the thickness of the metal sheet between the corners, thus making the connectors strong enough to hold the elements and easy to be cut off. Therefore, the elements remain firmly joined to the metal sheet by the connectors, but can be separated as highly accurate elements by smoothly cutting off the connectors.
The step of blanking the elements comprises the steps of placing the metal sheet on a die, and moving a pair of blanking punches toward the die to blank the elements out of the metal sheet, and the step of centering the metal sheet comprises the steps of pressing the metal sheet horizontally against a pair of counter punches mounted in the die for movement into and out of the die in alignment with the blanking punches, respectively, before the elements are blanked out of the metal sheet, the counter punches having respective slanted guide surfaces disposed so as to be aligned with the respective corners of the metal sheet and inclined downwardly toward the center of the metal sheet, and guiding the corners of the metal sheet along the slanted guide surfaces, respectively, to center the metal sheet.
The counter punches have the respective slanted guide surfaces for centering the metal sheet before the elements are blanked out of the metal sheet. Therefore, the metal sheet can be centered simply by pressing the metal sheet horizontally against the counter punches. Specifically, when the metal sheet is lowered toward the die, the corners of the metal sheet abut against the slanted guide surfaces of the counter punches. At this time, if the center between the corners of the metal sheet has been displaced to the left or right from a centered position, then one of the corners abuts against the slanted guide surface confronting the corner. Upon continued downward movement of the metal sheet in its horizontal attitude, the corner slides downwardly along the slanted guide surface, and the metal sheet moves in its horizontal attitude toward the centered position. The other corner abuts against the slanted guide surface confronting the other corner, so that the corners are positioned between the slanted guide surfaces. Inasmuch as the metal sheet is kept in its horizontal attitude and the corners are held against the respective slanted guide surfaces at the same positions, the center between the corners of the metal sheet is positioned as the centered position, thus centering the metal sheet. The metal sheet thus centered is then blanked by the blanking punches while its attitude is being maintained. Accordingly, the elements can be blanked highly accurately out of the metal sheet.
The metal sheet on the counter punches is centered before the metal sheet is blanked by the blanking punches. It is not necessary to center the metal sheet highly accurately with guide members which limit the opposite edges of the metal sheet to guide the metal sheet when the metal sheet is fed and charged into a position between the blanking punches and the counter punches. Since the clearance between the guide members and the metal sheet can be relatively large, any contact between the guide members and the metal sheet is reduced to allow the metal sheet to be delivered at a high speed for manufacturing the elements highly efficiently.
An apparatus for blanking elements out of a metal sheet according to the present invention is of a structure for carrying out the above blanking method. Specifically, the apparatus comprises a die for placing the metal sheet thereon, a pad for pressing the metal sheet against the die, a pair of counter punches mounted in the die for movement into and out of the die for abutting against a lower surface of the metal sheet at respective blanking positions thereon which are laterally spaced from each other, and a pair of blanking punches for lowering the metal sheet at the respective blanking positions thereon against the counter punches to blank the elements out of the metal sheet, the blanking punches having respective connector forming punches for forming the connectors in the respective thin portions of the metal sheet, the bodies having respective second edges remote from the first edge and formed in the respective thin portions of the metal sheet, the die having cavities defined therein at respective positions aligned with the connector forming punches, respectively, for accommodating the connectors respectively therein.
With the above arrangement, the elements are blanked out of the metal sheet pressed against the die by the pad by the blanking punches and the counter punches which cooperate with each other. At this time, the connector forming punches produce the connectors, allowing the elements to be blanked while remaining joined to the metal sheet by the connectors. The connectors are formed on the second edges, i.e., lower edges, of the bodies positioned in the thin portions of the metal sheet, by the connector forming punches. The connectors can thus be formed without causing a reduction in the accuracy of the V-shaped surfaces which need to be sheared highly accurately by the blanking punches.
The blanking punches are shaped to cooperate with the counter punches for blanking the elements out of the metal sheet substantially parallel thereto so as to be displaced in a blanking direction by a distance equal to at least the thickness of the metal sheet between the corners, the connector forming punches and the cavities being shaped to incline the connectors to the blanked elements and joined in opposite directions to the elements.
The elements are blanked, by the coaction of the blanking punches and the counter punches, out of the metal sheet substantially parallel thereto so as to be displaced in the blanking direction by the distance equal to at least the thickness of the metal sheet between the corners. Therefore, the elements are prevented from being fitted again in holes, complementary in shape to the elements, defined in the metal sheet after the elements are blanked. The connectors formed by the connector forming punches are inclined to the blanking direction along the inclination of the connector forming punched and the inclination of the cavities in the die. Consequently, the blanked elements have a thickness equal to the thickness of the portion of the metal sheet between the corners, and are highly rigid.
The connector forming punches are shaped to form the connectors each having a width which is 1 to 3 times the thickness of the metal sheet between the corners. When the connectors are formed by the connector forming punches, therefore, the width of the connectors can easily be made 1 to 3 times the thickness of the metal sheet between the corners.
The counter punches have respective slanted guide surfaces disposed so as to be aligned with the respective corners of the metal sheet and inclined downwardly toward the center of the metal sheet, for guiding the corners of the metal sheet along the slanted guide surfaces, respectively, to center the metal sheet when the metal sheet is pressed horizontally against the die by the pad before the elements are blanked out of the metal sheet by the blanking punches.
The metal sheet is lowered in its horizontal attitude toward the die by the pad, and the corners thereof are guided along the slanted guide surfaces of the counter punches. Thus, the metal sheet can reliably be centered with a highly simple arrangement.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.